Hi Gerald -
The first thing I'd suggest is to close & re-open the program, and do a hard shutdown & restart -- sometimes that fixes odd one-off glitches. If that doesn't help, try an older version of the project, or a backup copy, in case there's actually corruption in the file itself. Does the problem happen in all Dreamweaver files or projects or just the one? Did you change any Preferences, or upgrade any components of the application or the OS? If you can isolate the circumstances when the issue occurs,, then you'll have a better chance of potentially sussing it out..
You could also try resetting Dreamweaver's Preferences, as per this Adobe Help page..